Mule is an open source Enterprise Service Bus (ESB) and if you don't know what an ESB is you probably won't be interested in Mule or this book. If you do then the book has a lot to recommend it.

Far from being a distant, hands-off, view of the architecture of Mule it gets you into the code fairly quickly. A case study is used but most of the examples are still short enough for you to get the idea and they are well explained. There is scope, however, for an even simpler example at just above "hello world" level to get the complete beginner started.

The book covers Mule 2 but also points out differences between it and earlier versions. The first chapter introduces the main ideas of Mule and the next deals with actually getting the system running. From here we dive into the core of any ESB system - messaging.

Chapter Three covers messaging using email, web services, JMS, XMPP and so on. Chapter Four deals with routing and Chapter Five data transformation. The final part of the section introduces components.

The second part of the book puts the basics in practice and deals with topics such as deployment, security, logging, and reliability. The final section of the book looks at advanced topics such as using the Mule API, testing, scripting and tuning.

Overall this is the book you need if you plan to use or are using Mule. If you are less sure about picking Mule in the first place then a more general book on ESBs would be a better place to start.